Engine exhaust recirculation



United States Patent [72] Inventor .lorrna 0. Sarto 1,539,126 5/1925Link 123/119 Orchard Lake,Mlebignn 1,541,583 6/1925 Merz 123/119 [21]Appl. No. 807,705 1,860,641 5/1932 Woolson]... 123/119 [22] Filed March17,1969 2,154,417 4/1939 Anderson 123/119 [45] Patented Od- 24,19703,116,725 1/1964 Hadley 123/119 [73] Assignee Chrysler Corporation3,444,846 5/1969 Sarto et a1 123/119 mlhhnd Primary Examiner- Wendell E.Burns a corporation 0 D'hwm Attorney-Harness, Talburtt and Baldwin [54]ENGINE EXHAUST RECIRCULATION 40 claims 12 Drawing n ABSTRACT: Automobileexhaust gases are recycled by means of a bypass conduit communicatingwith the exhaust [52] m 123/119 system and discharging into the fuel andair inlet system in op- 15 I] Cl 25/06 position toa jet ofinlet'gasesdischargingthrough an orifice in [50] Field otSearch123/119A, the om valve when h l ne; is at the idle position, such 1 19that during engine idling, the bypass flow of exhaust gases into theinlet system is inhibited, but upon'o hing movement of [56] cud thethrottle valve from the idlepositiom tl ie jets move out of UNITEDSTATES PATENTS opposition with each other to enable increased exhaust1,432,751 10/1922 H8118" 123/1 19 ecycling'with increasing ngine'load,

Patented Nov. 24, 1970 3,542,003

VENT OR.

. partially burned ll ENGINE EXHAUST RECIIRQULATEKEN BACKGROUND ANDSUMMARY OF THE lNVEhlTlON reducing the oxides of nitrogen emitted fromthe exhaust It has been found that approxisystem into the atmosphere.mately percent exhaust gas recycling is required at moderate speeds tosubstantially reduce the nitrogen oxide content of the exhaust gasesdischarged in the atmosphere, that is, to below about 1000 parts permillion.

Although the prior art structures have had the desired effect ofreducing the content of nitrogen oxides in the exhaust by reducing themaximum combustion temperature in consequence of diluting the fuel-airmixture with recycled exhaust gases during certain operating conditionsof the engine, these structures have not been commercially acceptablefrom the standpoints of both cost and operating efficiency and have beencomplicated by the desirability of reducing the recycling duringconditions of both engine idling'when nitrogen oxide emission is a minorproblem andwide open throttle when maximum power is required, whileprogressively increasing the recycling of exhaust gases with increasingengine speed during cruising condition or with increasing engine load atpart open throttle. The nitrogen oxide emission isa direct function ofcombustion temperature and for that reason is less critical duringengine idling when the rate of fuel combustion and the consequentcombustion temperature are minimal, and during wide open throttleconditions which are ordinarily of short duration.

In the usual gasoline or hydrocarbon fuel type engine, fuel combustioncan take place at about 1200F. The formation of nitrogen oxides does notbecome particularly objectionable until the combustion temperatureexceeds about 2200F., but the usual engine combustion temperature whichincreases with engine load or the rate of acceleration at any givenspeed frequently rises to about 2500F. it is known that the recycling ofat least one-twentieth andnot more than one-fourth of the total exhaustgases through the engine, depending on the load or power demand, willreduce the combustion temperature to less than 2200F. The desired resultis usually obtained with the ordinary engine upon the recycling of about15 percent of the total exhaust gases during partially open throttle asaforesaid.

An important object of this invention is to provide improved meansuncomplicated by moving parts comprising a restricted recycling orbypass duct for recirculating a portion ofthe combustion products fromthe exhaust system to the inlet system of an automobile engine toovercome or avoid the problems and deficiencies of the prior art, aswell as to achieve a number of important results including preheatingand improved mixing and carburetion of the fuel-air mixture in the loadconditions, the total fluid flow through a fixed bypass orinlet header,the reduction of ice formation on the customary A throttle blade, andthe reduction of noxious nitrogen oxides in the exhaust.

Another object is to provide such a construction wherein the bypass ductextends in heat exchange relationship through thecustomary throttle bodyof the inlet system and terminates within the induction conduit in anozzle directed to discharge hot exhaust gases upstream against the flowof the fuel-air mixture in the induction conduit and also against theusual throttle valve, thereby to provide simple, economical andeffective means for accomplishing the foregoing as well as forpreheating the throttle body and simultaneously cooling the exhaustgases in the bypass conduit below the fuel ignition temperature, and fordiluting the fuel-air mixture with substantially incombustible exhaustgases to lower the combustion temperature in the engine and therebyreduce the formation of nitrogen oxides during the combustion process.

Another and more specific object is to provide an exhaust recyclingsystem comprising a bypass duct which opens within the induction conduitso as to discharge the exhaust gases against an oppositely directedstream of inlet gases when the throttle valve is in its idle operatingposition. The stream of inlet gases may be effected, for example, bymeans of a restricted inlet gas orifice in the customary butterfly typethrottle valve. The bypass duct terminates adjacent the downstream'side'of the throttle valve in opposition to the inlet gas orifice,whereby the recycling of exhaust gases is rendered nominal during idleoperation. However the bypass duct has a fixed restriction dimensionedso that more than 5 percent but less than approximately 25 percent andusually about 15 percent of the total exhaust gases are conductedthrough the bypass duct when the throttle is partially open and theeffective pressure differential between its ends. corresponds tocruising or part open throttle acceleration conditions.

By virtue of the foregoing, communication will exist at all timesbetween the exhaust and inlet systems and a portion of the hot exhaustgases will be directed against the throttle valve to prevent or minimizecarburetor icing during fast idling of a cold engine when ice formationis most likely to occur. During cold engine idling when the throttle isheldpartially open by the usual fast idle cam during this condition, asis customary, the flow of hot exhaust gases againstthe throttle bladewill increase, as compared to normal warm idling, because the increasedengine speed at fast idle will increasethe gas pressure in the exhaustsystem and the opposed gas jets from the bypass duct and throttleorifice will move partially out of the opposing alinement that existwhen the throttle valve is at its normal warm idleposition;

In addition, within the range from idle to light or moderate recyclingorifice of the type comprising the present invention increases at anygiven engine speed with increasing engine load. For example in aconventional automobile engine, the pressure downstream of the throttlevaries roughly in the neighborhood of from one-half atmosphere duringidling to approximately one atmosphere at wide open throttle, while theexhaust pressure simultaneously varies roughly from one to twoatmospheres. These factors compensate for the increasing combustiontemperature with increasing load and result in a desirable increase inthe effectiveness of the exhaust recycling through the fixed bypassrestriction with increasing load or acceleration.

As the engine load-or acceleration decreases and the speed increases tothe cruising condition, the combustion temperature and the pressuredifferential across the fixed bypass I restriction, as well the as thetotal quantity of exhaust gases, decrease and the rate of exhaustrecycling declines for improved fuel economy, again as desired becauseless recycling is required to maintain the combustion temperature belowthe level at which nitrogen oxide formation is objectionable. As thepressure differential between the inlet and exhaust headers increaseswith increasing load, the effective resistance of the fixed restrictionto the recycling flow increasesbecause the flow rate variesapproximately as the square root of thepressure differential. Thus atwide open throttle, the proportion of the total exhaust gases that isrecycled is somewhat lessthan the proportion recycled at partially openthrottle. This factor also is as desired because the customary excessfuel enrichment at wide open throttle in cooperation with therecycled'exhau st gases is adequate to prevent overheating during thecombustion process and reduce the formation of nitrogen oxides to thetolerable level.

A more specific object is to provide an exhaust recycling system whereinthe restricted orifice in the throttle valve opens into a duct carriedby the throttle valve. This latter duct choice of location of the bypassduct is liberalized, and the I latter may be centered more convenientlywithin the induction conduit and its upstream end located below the baseof the throttle body to prevent damage prior to assembly of thecarburetor and engine.

Other objects are to provide the restriction for the bypass ductadjacent its upstream end, as for example at its communication with theexhaust system, where the accumulation of deposits from the exhaust isminimized; and to locate the upstream end of the bypass duct within aventuri portion of the exhaust system, as for example adjacent theexhaust valve seat where the speed of exhaust flow is a maximum, therebyto pro vide means for decreasing the effective pressure differentialbetween the ends of the bypass conduit, or in fact if desired to reversethe direction of the pressure differential (with respect to thecustomary pressure differential at idle) during engine operation underhigh load. Thus the recycling of exhaust gas may be reduced at wide openthrottle for example when maximum power is desired orin the situationwhereit is desirable to reverse the pressure differential with respectto the usual BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematicfragmentary cross-sectional view, as

also are FIGS. 2 and 3, through three different automobile engineinduction systems showing three embodiments of the downstream ends ofthe exhaust bypass duct.

FIGS. la, 2a, and 3a are similar views showing modifications of theupstream ends of the bypass duct.

FIGS. 4 through 9 are schematic fragmentary cross-sectional viewsshowing additional modifications of the present invention.

It is to be understood that any one of the downstream ends of the bypassconduit shown in the aforesaid views can be employed with any one of theupstream ends thereof, the desired amount of exhaust recirculationduring different engine operating conditions being obtained bypredetennining the dimensional and angular relationships of thecooperating parts, including the venturi restrictions in the exhaustsystem and the location of the bypass duct restriction and the upstreamand downstream openings of the bypass duct into the venturi restrictionand inlet induction conduit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings,particularly FIGS. 1 and In, an application of the present invention isillustrated by way of example with an automobile engine 9 having acarburetor 10 providing the inlet fuel-air induction conduit 11, whichcomprises the upstream portion of an inlet header 12 for supplying acombustible fuel and air mixture to the engine cylinders 13. Thecarburetor 10 may comprise any conventional type which has the usual airinlet at the upstream end of the induction conduit 11, the usual fuelmetering system and nozzles or jets for supplying idle and operatingfuel to the conduit 11 during various operating conditions and forenriching the fuel supply during acceleration and wide open throttle,and the usual automatic choke (includingchoke valve 11a) andthermostatic means for controlling idle enrichment and fast idleoperation during cold starting conditions. An example of such acarburetor is illustrated by way of example in Ball, U.S. Pat. No.2,966,344, so that the foregoing conventional features disclosed in thelatter patent are incorporated herein by reference and are not describedin detail.

The downstream portion of the induction conduit 11 comprised thecustomary throttle body containing the conventional butterfly typethrottle valve 14. The inlet fuel-air mixture is conducted via theheaders or manifolds 12a and 12b, comprising extensions of the header12, to the left and right banks of cylinders 13 respectively in timedrelation with operation of the engine pistons 15. After combustion ofthe fuel-air mixture above the pistons 15, the exhaust gases areconducted in timed relationship with respect to the reciprocation of thepistons 15 and exhaust valves 18 to the exhaust manifolds or headers 17,which may discharge through an afterburner or exhaust reactor 16 andthence through a muffler to the atmosphere. The exhaust reactor orafterburner 16 operates to complete the combustion of incompletelyburned fuel before discharging the exhaust to the atmosphere, and may besupplied with additional fuel and air to facilitate combustion thereinin accordance with known practice.

The left and right manifolds 17 are connected by a crossover conduit 19which conducts the hot exhaust gases into heat exchange relationshipwith portions 20 of the wall of the inlet header. The wall portions 20extend transversely to the direction of flow of the inlet mixture andare commonly referred to as the hot spot which preheats the inletmixture and enhances vaporization and mixing of liquid fuel droplets. Athermostatically controlled valve 21 in one header 17 controls the flowof hot gases in the crossover conduit 19 so as to expedite heating ofthe hot spot 20 during the engine warrnup period and to preventoverheating during operation of the engine under load. The structuredescribed thus far may be conventional.

Associated with the throttle valve 14 and extending through the hot spot20 is arestricted nozzle 22 connected by means of a bypass or recyclingconduit 23 with the exhaust header 17 at a location proximate theannular seat for valve 18 which connects the upper end of cylinder 13with header 17. A venturi effect at the restricted opening defined bythe annular seat for valve 18 results in a reduced pressure at thelocation of the opening of conduit 23 into header 17, so that duringperiods of high engine load, as for example near wide open throttleconditions, the effective static pressure at said opening causing bypassflow of exhaust gases through nozzle 22 will be reduced with respect tothe total exhaust pressure in header 17. At the same time, the increasedinlet pressure within conduit 11 at the region of nozzle 22 and thecorresponding increased rate of inlet flow of fuel and air opposing theexhaust jet from nozzle 22 at or near wide open throttle conditionseffectively reduces the recycling of exhaust gases into the inductionconduit.

The reduced exhaust recycling at high engine load conditions isaccomplished both by reason of the reduced efiective. pressuredifferential across the nozzle 22 and the increased rate of inlet flowdynamically opposing the upwardly directed exhaust jet from nozzle 22adjacent the under portion of throttle valve 14. These factors may bepredetermined to achieve a reverse flow through nozzle 22 at or nearwide open throttle conditions, whereby a highly combustible mixture offuel and air is added to the exhaust header 17 by aspirator action tofacilitate complete combustion of the exhaust products in the reactor16.

For operation during normal cruising conditions, the nozzle 22 has afixed restriction dimensioned to enable controlled recycling of aportion of the exhaust gas into the inlet fuel-air to pass 'at least 5percent and not more than 25 percent of the total exhaust gases,depending upon the specific engine and its operating conditions. In theusual situation effective reduction of nitrogen oxides in the exhaust isaccomplished by recycling approximately 15 percent of the exhaust gasesas aforesaid, preferably through several nozzles 22 arranged in themanner of the nozzle shown where a multiple barrel carburetor isinvolved.

In climatic regions where icing is a problem, each nozzle 22 may beextended into proximity with its associated throttle valve 14 by meansof an integral low resistance tubular stand pipe having a lengthdepending upon the specific geometry 1 proved breaking up,

and location'of the portion of the hot spot through which it extends.Each bypass conduit 22, 23 thus has the same resistance to gas flow. Theflow of the hot exhaust gases through the hot spot 20 and nozzle 22 alsofacilitates preheating of the hot spot 20 and throttle valve 14 toassure vaporization of the inlet mixture and the prevention of iceformation adjacent the edges of the throttle valve 14. Simultaneouslythe recycled exhaust gases are cooled below the ignition temperature ofthe combustible inlet mixture. To this end the nozzle 22 is preferablyof heat conducting material and is sufficiently long to achieve thenecessary heat transfer from the exhaust gases to the hot spot and inletmixture. Also by directing the exhaust gases directly in opposition tothe flow of the inlet mixture, im-

droplets are achieved with consequent improved mixing of the combustibleinlet gases and uniform predictable combustion characteristics withincylinders 13.

A modification of the exhaust recycling system is illustrated in FIG. 2wherein the exhaust jet is directed-angularly into induction conduit 11through nozzle 22a located upstream of the choke valve 11a, which isalso upstream of the conventional fuel nozzles discharging into conduit11. By predetermining the angle of the nozzle 22a and its restriction, abalance between static and dynamic pressures can be obtained forcontrolling the recycling of the exhaust gases under various engineoperating conditions. The lower end of duct 23 communicates with exhaustheader 17 at the location of a venturi restriction 24 for operationsubstantially as described above. In FIG. 2a, the venturi restriction 24is located sufficiently remote from valve 18 so as to minimize pressurepulsing that occurs on the region of valve 18 in consequence of itsopening and closing. Where the pressure pulsing is not objectionable,the lower end of conduit 23 in FIG. 2 may be located as described withreference to FIG. 1a and of course the lower end of conduit 23 in FIG. 1can readily be located as illustrated in FIG. 2a.

In FIG. 2, direct heating of throttle valve 14 is not as effective as inFIG. 1, but the FIG. 2 construction is preferred where it is desirableto add clean air without fuel to header 17 during wide open throttleconditions by causing reverse flow in bypass duct 23 from inductionconduit 11 to header 17, so as to increase the efficiency of the exhaustreactor 16 in combusting exhaust products before these are discharged tothe atmosphere.

In other respects, the structure of FIG. 2 operates to accomplishsubstantially the same exhaust recycling as in FIG. '1. In bothstructures, the exhaust recycling during normal idle is a minimum, whenthe formation of noxious nitrogen oxides during combustion is also aminimum. During partly-open throttle conditions, the effective pressuredifferential between the exhaust pressure in header 17 and the inletpressure in conduit 11 and the resulting rate of exhaust recycling willincrease as the throttle opening increases, so as to effect the desiredamount of exhaust recycling until at or near wide open throttle, theventuri effect at the lower end of conduit 23 substantially reduces theexhaust recycling. Also in both structures, a reverse flow of fuel andair (FIG. 1) or clean air (FIG. 2) from conduit 11 to header 17 andreactor 16 may be effected if desired at wide open throttle conditions,depending on the arrangement and relative dimensions of the partsinvolved, especially the restrictions for nozzles 22 and 22a and theangles of their respective jets into the inlet conduit 11, and theeffectiveness of the venturis described.

FIGS. 3 and 3a illustrate other modifications of the exhaust recyclingsystem wherein the overall arrangements of the engine 9 and inlet systemll, 12 and exhaust system 17, 19 are the same as above described.Instead of connecting the lower end of conduit 23 at the region of aventuri as in FIGS. la and 2a, conduit 23 terminates in a pitot-typeopening 25 within header 17, so as tobe responsive to the velocity forceor pressure of the exhaust flow, as well as the static pressure of theexhaust. This arrangement is particularly suitable for trucks thatusually operate at high engine load, or for small engines dispersion andvaporization of liquid fuel that seldom operate at low pressure inconduit 11. The pitot or total pressure opening 25 compensates for thehigher pressure in conduit 11.

In FIG. 3, the upper end of conduit 23 terminates in a restricted nozzle22b. The nozzle 22b extends through the throttle body 26 in heattransfer relationship therewith at a location between the customarygaskets'28 and 27 which serve to insulate the throttle thermally fromthe adjacent manifold 12 and upper portion of the conduit 11 thereby toenable controlled heating of the throttle body 26 in accordance with theextent of bypass flow or exhaust recirculation. An enlargement in theconduit 23 comprising a chamber 29 formed in throttle body 26predetermines the throttle body surface in heat exchange relationshipwith the exhaust bypass flow.

' The nozzle 22b is directed angularly toward and terminates adjacentthe throttle valve 14 when the latter is at its idle position shown anddirects a jetof exhaust gases in opposition to a jet of inlet gasesflowing through a restricted opening 30 in valve 14, FIG. 4. The opening30 may comprise part of the idle air supply for the engine, especiallyduring fast idle, and is dimensioned with respect to the dimensions ofthe exhaust bypass duct system to substantially block exhaustrecirculation when the throttle valve 14 is at its warm idle positionshown.

As valve 14 progressively opens with increasing engine load, theopposing jets from nozzle 22b and orifice 30 move out of alinernent theeffective pressure differential across orifice 30 decreases, and wherethe lower upstream end of duct 23 comprises the pitot opening 25, thepressure differential between ,the'latter end and the discharge openingof nozzle 22!: in-

creases, all to the end of increasing the bypass flowor exhaustrecirculation from header 17 into conduit 11. Also during part Ithrottle opening, the upper open end of nozzle 22b is protected bythrottle valve 14 from the dynamic or velocity pressure of the inletgases. At wide open throttle, dotted position, FIG. 4, the upper end ofnozzle 22b is exposed to the inlet velocity flow in the manner of apitot tube, thereby to oppose the pitot action at end 25 and reduce theexhaust recirculation.

with a bypass conduit 23 having a lower end opening at a venturi portionof header 17 as in either FIG. 1a or FIG. 2a.

In other respects, the exhaust recirculation is the same as in FIG. 4.Structures similar to those shown in FIGS. 1 and 2 for example may alsobe employed where heating of the throttle body 26 is to be minimized.

FIG. 6 illustrates a nozzle 22c extending directly from the exhaustcrossover conduit 19 and having'its restriction at its lower end openingflush into conduit 19. Thus nongaseous combustion products cannotreadily enter and accumulate within the nozzle and clog the bypasssystem. Where the ex haust contains appreciable quantities of materialsthat tend to form gummy residues upon cooling, as for example in givingup heat to the hot spot 20, FIG. 1, or throttle body 26, FIG. 4,

these residues have less tendency to deposit within the hot passage 19or header 17 than in the cooler nozzle 22b, for example. Where desiredthe restriction in the bypass conduit 23 illustrated in the other FIGS.can be made at the juncture with either header 17 or 19 as the casemight be. In other respects the nozzle structure of FIG. 6 cooperateswith the opposed jet passing through throttle orifice 30 as described inregard to FIGS. 3, 4 and 5.

FIG. 7 illustrates a construction-wherein the bypass nozzle 22d extendsdirectly from the cross over conduit 19, as in FIG. 6, and the exhaustjet therefrom is opposed by an inlet jet directed from throttle orifice30 through a nozzle 31 integral with throttle blade 14. An advantage ofthis structure is that the effect of a slight opening movement of valve14, in moving It is apparent that the nozzle 22b of FIG. 4 can beemployed 1' the opposed jets of inlet and exhaust gases out of opposingalinement is magnified. Thus at fast idle conditions when valve 14 isopened only slightly, phantom position, FIG. 7, the jet of exhaust gasesinto conduit 11 from nozzle 22d is no longer opposed by the jet of inletgases through nozzle 31. In consequence, exhaust recirculation will beeffective to warm the throttle valve 14 and prevent icing during thecold engine operating condition when fast idle is required.

When the engine warms to its normal idle operating condition, thethrottle valve 14 will close to its warm idle condition shown in solidlines. The opposing jets will then reduce the exhaust recirculation.Also, in accordance with the structure shown, the nozzle 31 canterminate at any reasonably desired position, so that the nozzle 22d canbe located. at any desired position and can be readily centered withinthe conduit II to minimize distortion of the customary inlet flow. Alsothe nozzle 22d can terminate below the level of gasket 28, so as to beprotected against accidental damage prior to and during assembly of theupper portions of the carburetor, including throttle body 26.

It is apparent that the lower end of the bypass nozzle or conduit 23illustrated in any one of FIGS. 4 through 7 can be connected with theexhaust header system as illustrated in any one of the preceding FIGS.,in accordance with the mode of operation desired and the specificrequirements of the particular engine.

FIG. 8 shows a modification where the inlet nozzle 31 terminates offcenter of the axis of the induction conduit 11 so as to oppose anangularly directed nozzle 22c of the bypass duct means 23. The lowerupstream end of duct 23 may be connected with the exhaust header systemas illustrated in any of the preceding FIGS. A slight opening movementof throttle 14 from the normal warm idle position shown, as for exampleto a.

fast idle position, will move the opposed nozzles 22e and 31 out ofalinernent and tend to increase the exhaust gas recycling through theconduit 23. Also as illustrated particularly in FIGS. 1, 3, 4, and 6,the throttle 14 shields the upper end of nozzle 22a from the inlet flowthrough induction conduit 11 during part open throttle conditions, butexposes the nozzle 22e to the velocity pressure of the inlet flow atwide open throttle so as to inhibit exhaust recirculation.

FIG. 9 shows a modification wherein the bypass duct 23 opens into theexhaust header system at the region of the crossover passage 19, so asto pass through the hot spot as described with reference to FIGS. 1, 6and 7 for example. The upper or downstream end of the bypass duct 23 maybe connected with the inlet header 11 in any of the ways illustrated inthe preceding FIGS.

Iclaim:

I. In an internal combustion engine:

A. an inlet header for conducting'a fuel-air mixture into said enginefor combustion therein;

B. an exhaust header for discharging the combustion products from saidengine;

C. and means for effectively inhibiting the formation of noxious oxidesofnitrogen during said combustion by limiting the temperature thereofcomprising restricted bypass duct means having:

1. one end opening into said exhaust header to receive exhaust gases;and

2. a second end opening into said inlet header to discharge ajet of saidexhaust gases thereinto;

D. a throttle valve in said inlet header for controlling the flow ofsaid fuel-air mixture therein, said throttle valve having a restricted:

l. orifice extending therethrough for directing a jet of inlet gases inopposition to said jet of exhaust gases when said throttle valve is atan idle position; and

2. said orifice being movable with said throttle valve to direct saidjet of inlet gases out of opposition with said jet of exhaust gases uponopening movement of said throttle valve from said idle position.

2. In an engine according to claim 1, said throttlevalve comprising ablade-type valve having said orifice extending through the bladethereof, said second end of said bypass duct terminating adjacent saidorifice at the downstream side of said blade at the idle position.

3. In the combination according to claim l, the restriction in saidbypass duct being at the opening thereof into said exhaust header.

4. In the combination according to claim 1, said one end of said bypassduct opening into said exhaust header adjacent a restricted regionthereof to reduce the static pressure at said one end when the exhaustgas flow in said exhaust header approximates wide open throttle engineoperation.

5. In the combination according to claim 4, said engine having acylindrical combustion chamber, a piston reciprocable within saidcombustion chamber, and a valve controlled restricted opening connectingsaid chamber and exhaust header for discharging exhaust gases thereintofrom said chamber, said restricted region of said exhaust headercomprising said valve controlled opening.

6. In an engine according to claim 3, said restricted region of saidexhaust header and said bypass duct being dimensioned to effect a flowof inlet gases from said inlet header to said exhaust header during wideopen throttle operating conditions for said engine.

7. In the combination according to claim 2, said orifice comprising aninlet duct carried by and extending downstream of said blade toterminate adjacent said second end of said bypass duct to direct saidjet of inlet gases in opposition to said jet of exhaust gases when saidthrottle valve is at its idle position.

8. In the combination according to claim 7, said second end of saidbypass duct extending coaxially into the portion of said inlet headerimmediately downstream of said throttle valve.

9. In the combination according to claim 1, said inlet header includinga throttle body portion having said throttle valve mounted therein andspaced from the adjacent downstream portion of said inlet header by aheat insulating gasket, said bypass duct having a portion containedwithin the sidewall of said throttle body to heat the latter by saidexhaust gases.

10. In the combination according to claim 1, said inlet header includinga throttle body portion having said throttle Ill. In the combinationaccording to claim I, said inlet header including a throttle bodyportion having said throttle valve mounted therein and spaced from theadjacent downstream portions of said inlet header by a heat insulatinggasket to reduce conduction of engine heat to said throttle body, thesecond end .of said bypass duct terminating downstream of said gasket,and said orifice comprising an inletduct carried by said throttle valveand extending downstream thereof within said inlet header andterminating adjacent said second end to direct said jet of inlet gasesin opposition to said jet of exhaust gases when said throttle valve isat its idle position.

I2. In the combination according to claim 1, said one end of said bypassduct comprising a pitot-type opening subject to the velocity pressure ofthe exhaustgas flow in said exhaust header.

13. In an engine according to claim 12, said throttle valve comprising ablade-type valve having said orifice extending through the bladethereof, said second end of said bypass duct terminating adjacent saidorifice at the downstream side of said blade at the idle position.

14. In the combination according to claim 2, said engine comprising anautomobile engine, said second end comprising a pitot-type openingdirected in an upstream direction within blade is at a wide openthrottle position and shielded from said velocity pressure when saidblade is at a part throttle opening corresponding to cruising condition.

15. In the combination according to claim 2, said exhaust header havinga portion extending transversely to the flow of inlet gases in saidinlet header downstream of said throttle valve to provide a hot wall ofsaid header portion for impingement of said inlet gases thereagainst,said bypass duct opening into the last named portion to receive exhaustgases therefrom and extending through said hot wall to facilitateheating thereof.

16. In the combination according to claim 15, the restriction in saidbypass duct being at the opening thereof into said headerportion.

17. Inthe combination according to claim 2, the restriction 18. In thecombination according to claim 4, said throttle valve comprising ablade-type valve having said orifice extend- I comprising an automobileengine, said second end comprising a pitot-type opening directed in anupstream direction within said inlet header and at a location withrespect to said blade exposed to the velocity pressure of the inletgases when said blade is at a wide open throttle position and shieldedfrom said velocity pressure when said blade is at a part throttleopening corresponding to cruising condition.

20. In the combination according to claim 19, said restricted region ofsaid exhaust, header and said bypass duct being dimensioned to effect aflow of inletgases from said inlet header to said exhaust header duringwide open throttle operating conditions for said engine.

21. In the combination according to claim 5, said inlet header includinga throttle body portion having said throttle valve mounted therein andspaced from the adjacent downstream portion of said inlet header by aheat insulating gasket, said bypass duct having a portion containedwithin the sidewall of said throttle body to heat the latter by saidexhaust gases.

22. In the combination according to claim 21, said throttle valvecomprising a blade-type valve having said orifice extending through theblade thereof, said second end of said bypass duct terminating adjacentsaid orifice at the downstream side' of said blade at the idle position.

23. In the combination according to claim 5, the restriction in saidbypass duct being at the opening thereof into said exhaust header.

24. In the combination according to claim 1, said second end comprisinga pitot-type opening directed in an upstream direction within said inletheader at a location exposed to the velocity pressure of the inlet gaseswhen said valve is wide open;

25. In the combination according to claim 24, said'throttle valvecomprising a blade type valve having said orifice extending throughtheblade thereof, said second end of said bypass duct terminatingadjacent said orifice at the downstream side of said blade at the idleposition, said second end being located at a position shielded by saidblade from said velocity pressure when said valve is at a part throttleposition.

26. In the combination according to claim 24, said bypass duct beingdimensioned to effect a flow of inlet gases from said inlet header tosaid exhaust header during wide openthrottle' operation of said engine.

27. In the combination according to claim 24, said one end of saidbypass duct comprising a pitot-type opening subject to the velocitypressure of the exhaust gas flow insaid exhaust header.

28. In the combination according to claim 27, said throttle said inletheader to said exhaust header during wide open throttle operation ofsaid engine.

30. In the combination according to claim 29, said throttle valvecomprising a blade-type valve having said orifice extending through theblade thereof, said second end of said bypass duct terminating adjacentsaid orifice at the downstream side of said blade at the idle position.

31. In the combination according to claim 7, said exhaust header havinga portion extending transversely to the flow of inlet gases in saidinlet header downstream of said throttle valve to provide a hot wall ofsaid header portion for impingement of said inlet gases thereagainst,said bypass duct opening into the last named portion to receive exhaustgases therefrom and extending through said hot wall to facilitateheating thereof.

32. In the combination according to claim 31, said inlet headerincluding a throttle body portion having said throttle valve mountedtherein, the second end of said bypass duct terminating downstream ofsaid throttle body.

33. In the combination according to claim 7, said one end of said bypassduct opening into said exhaust header adjacent a restricted regionthereof to reduce the static pressure at said one end when the exhaustgas flow in said exhaust header approximates wide open throttleengineoperation.

34. In the combination according to claim 33, said engine having acylindrical combustion chamber, a piston reciprocable within saidcombustion chamber, and a valve controlled restricted opening connectingsaid chamber and exhaust header for discharging exhaust gases thereintofrom said chamber, said restricted region of said exhaust headercomprising said valvev controlled opening.

35. In the combination according to claim 33, said restricted region ofsaid exhaust header and said bypass duct being dimensioned to effect aflow of inlet gases from said inlet header to said exhaust header duringwide open throttleoperating conditions for said engine.

36. In the combination according to claim 7, said engine comprising anautomobile engine, said second end comprising a pitot-type openingdirected in an upstream direction within said inlet header and at alocation with respect to said blade exposed to the velocity pressure ofthe inlet gases when said blade is at a wide open throttle position andshielded from said velocity pressure when said blade is at a partthrottle opening corresponding to cruising condition. 37. In thecombination according to claim 7, said one end of said bypass ductcomprising a pitot-type opening subject to the velocity pressure of theexhaust gas flow in said exhaust header.

38. In the combination according to claim 37, said second end comprisinga pitot-type opening directed in an upstream direction'within said inletheader at a location exposed to the velocity pressure of the inlet gaseswhen said valve is wide therewith.

